In hydroxyapatite

The estimation of the crystallinity index (Cl) of bone is based on one of the four vibrational modes associated with the apatite phosphate group. In amorphous calcium phosphate, the absorption band at 550-600 cm-1 appears as a single broad peak, whilst in hydroxyapatite it is split into bands of unequal intensity by the apatite crystal field (Sillen and Parkington 1996). Based on the splitting factor introduced by Termine and Posner (1966), Weiner and Bar-Yosef (1990) proposed the use of a crystallinity index to measure the crystallinity of bone mineral. As illustrated in Fig. 4.7, the Cl is estimated by drawing a base line from 750 to 495 cm 1 and measuring the heights of the absorption peaks at 603 cm-1 (measurement a), 565 cm 1 (measurement b) and the distance from the base line to the lowest point between the two peaks (c). Cl is calculated from the formula ... 

C. B. Baddiel, E.E. Berry, Spectra-structure correlations in hydroxyapatite and fluor-apatite, Spectrochim. Acta 22 (1966) 1407-1416. 

F. Freund, R.M. Knobel, Distribution of fluorine in hydroxyapatite studied by infrared spectroscopy, J. Chem. Soc. Dalton 11 (1977) 1136-1140. 

Another example is LIBS application for real-time identification of carious teeth (Samek et al. 2003). In the dental practice, usually more healthy tissue is removed than ultimately necessary. Carious and healthy tooth material can be identified through the decrease of matrix elements Ca and P in hydroxyapatite and/or the increase of non-matrix elements, typically Li, Sr, Ba, Na, Mg, Zn and C, using pattern recognition algorithms. A fiber-based LIBS assembly was successfully used for this task. As for the case of phosphate ores evaluation, the efforts aimed at normalizing the spectrum collection conditions and procedures, so that the spectra are sufficiently reproducible for precise quantitative... 

Laurencin et al. studied the substitution of Mg for Ca in hydroxyapatite, combining H, Mg, and Ca solid-state NMR results (all nuclides at natural abimdance) and DPT calculations of the NMR parameters associated with each nuclide. Despite the reported difficulties in achieving good-quality spectra (even at 19.6T) from samples with small... 

Person 1 Use Bragg s Law [Eqnation (1.35)] to calculate the rf-spacing (in nm) for the first diffraction peak in hydroxyapatite. Assume a first-order diffraction and an X-ray source of k = 0.1537 nm. 

Signal D gD = 1.9973 = g (orthorhombic C02 ) The orthorhombic and axial C02 molecular ions were detected in CaC03 and NaHC03 (nahcolite) as well as in hydroxyapatite (tooth enamel)... 

Boskey, A., Posner, A, S. The role of synthetic and bone extracted Ca-Phospholipid-PC>4 complexes in hydroxyapatite formation. Calc. Tiss. Res. 23, 251 (1977)... 

The different functions of the gla proteins and phosphoproteins must be related to the packing in hydroxyapatite and apatite [Ca2(OH)(P04)J,but probably depend too on the relative disposition of the oxygen donors in the gla and phosphoryl groups. 

The effect of pH on solubility is also important in understanding how fluoride ion reduces tooth decay. When tooth enamel comes in contact with F ions in drinking water or fluoride-containing toothpaste, OH- ions in hydroxyapatite, Ca5(PC>4)30H, are replaced by F- ions, giving the mineral fluorapatite, Ca5(PC>4)3F. Because F- is a much weaker base than OH-, Ca5(P04)3F is much more resistant than Cas(P04)30H to dissolving in acids. 

One of the important fields where carbohydrate polymer/inorganic hybrids may be successfully applied is bioactive materials, e.g., artificial bones expedient for surgery to accelerate the recovery of living bones. There has been increasing interest in hydroxyapatite (HAp) deposition onto the matrix surface of cellulose or related polysaccharide. HAp is a form of calcium phosphate, a main constituent of the inorganic phase of human bone. This kind of study is also a step on the way to exploitation of new biomimetic mineralization methods. 

The F content in recent bone or dentine apatite is normally less than 0.1 wt.%. For ancient specimen, F is known to diffuse during burial into bone material. Its enrichment is generally a part of many complex diagenetic changes of bone and tooth, which remains after their deposit. Fluorine can react with the bone and dentine mineral phase to form calcium fluoride compounds. It usually substitutes for hydroxyl ions in hydroxyapatite, leading to the less soluble fluorapatite compound (Ca10(PO4)6(F)2, FAP). 

The fraction of DNA that remains single-stranded in hydroxyapatite fractionation can be calculated as follows ... 

As a result, the need for SnF2 has decreased from 500,000 lbs/year to less than 20,000 lbs/year. While sodium monofluorophosphate still being comparatively less expensive, it has a worldwide market of over two million pounds/year. The comparative study of Hayden shows that sodium monofluorophosphate is approximately twice as effective as NaF in inhibiting acid production in a saliva-glucose mixture [105], It is believed that the cavity prevention provided by fluoride ions is due to the replacement of hydroxyle group in hydroxyapatite, Ca5(P04)30H of the tooth by fluoride ions to forms more insoluble fluoroapatite, Ca5(P04)3F [106],... 

Dietz, V. R., Rootare, H.M., and Carpenter, F.G. The surface composition of hydroxyapatite derived from solution behaviour of aqueous suspensions. J. Coll. Sci. 19, 87-101 (1962). Rootare, H.M., Dietz, V.R., and Carpenter, F.G. Solubility product phenomena in hydroxyapatite water systems. J. Coll. Sci. 17, 179-206 (1962). 

The mechanism by which fluoride prevents caries is not clearly understood. It is known that the fluoride ion (F ) can replace the hydroxyl ion (OH ) in hydroxyapatite. 

Figure 9.1. Influence of the MAS speed on the H NMR linewidth from OH groups and molecular water in hydroxyapatite. Note the marked effect on the OH protons reflecting the homonuclear dipolar contribution. After Yesinowski and Eckert (1987), by permission of the American...

Cho G, Yesinowski JP (1993) Multiple-quantum NMR dynamics in the quasi-one-di-mensional distribution of protons in hydroxyapatite. Chem Phys Lett 205 1-5... 

Figure 9.43 Raman spectra of plasma sprayed calcium phosphate coating shows the difference in hydroxyapatite content by comparing intensity of the OH stretching band at (a) near substrate (b) in the middle and (c) near the surface of the coating layer.

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